In the design of tiltcab trucks, it is desirable to provide a suspension system between the truck cab and the truck frame to partially isolate the occupants of the truck cab from vibration and jolts due to unevenness in the roads over which the truck passes. However, if the tilt cylinder(s) are connected directly to the cab frame and the truck frame, as is most convenient, the incompressible fluid in the push and pull chambers of the tilt cylinder(s) tends to hold the cab rigidly in position relative to the truck frame. This problem is conventionally overcome by providing hydraulic lost motion apparatus which permits hydraulic fluid to move back and forth between the push chambers and the pull chambers of the tilt cylinder(s) while the truck cabs are in their "over-the-road" position, thereby permitting the cabs to pivot relative to the frames to accomodate vertical motion in the suspension system. Examples of such apparatus are shown, for instance, in published United Kingdom patent application No. 2,048,383A and West German Off. No. 2,458,264.